1. Field of the Invention
The present invention relates to a piezoelectric device, a droplet jetting device that uses the same, and an image output device.
2. Description of the Related Art
A piezoelectric element (electrostrictive element) is an element that vibrates according to an electric signal or that generates an electric signal according to its own vibration caused by an external force. JP 11-191645 (reference 1) and JP 2003-069103 (reference 2) disclose devices that include such a piezoelectric element respectively.
The device disclosed in the reference 1 is an example of a piezoelectric/electrostrictive actuator. FIG. 14A is a perspective view of a configuration of the actuator. The piezoelectric/electrostrictive actuator comprises a thin substrate 61, an intermediate layer 62, a piezoelectric/electrostrictive film 63, an electrode film 64, and an electrode 65. The piezoelectric/electrostrictive film 63 is provided between the electrode layer 64 and the intermediate layer 62 and the piezoelectric/electrostrictive film 63 is connected to an external device (not shown) through the electrode 64 with a lead wire and through the intermediate film 62, the thin substrate 61 and the electrode 65. And, according to an electric signal output from an external device and applied to the electrode film 64 and the intermediate layer 62 respectively, the piezoelectric/electrostrictive film 63 vibrates.
FIG. 14B is a perspective view of the piezoelectric/electrostrictive actuator disclosed in the same document, which is applied to an ink jet print head. The ink jet print head 60 comprises a thin substrate 61, an intermediate layer 62, a piezoelectric/electrostrictive film 63, an electrode film 64, and an electrode 65, a recess 66, and a partition wall 67. Portions above the thin substrate 61 are the same as those shown in FIG. 14A. The recess 66 and the partition wall 67 are provided under the thin substrate 61.
The reference 2 discloses an example of a piezoelectric/electrostrictive actuator that includes a piezoelectric element. FIG. 16 is a top view of the configuration of the piezoelectric/electrostrictive actuator. The piezoelectric/electrostrictive actuator is configured by a flexible printed wiring board 71, a plurality of bumps 78, a plurality of electric wirings 79, and a plurality of actuator elements 74.
FIG. 17 is a cross sectional view of the piezoelectric/electrostrictive actuator shown in FIG. 16 the X-X′ line. The piezoelectric/electrostrictive actuator is configured by a plurality of core members 72, a plurality of junction materials 73, a plurality of actuator elements 74, a plurality of signal electrodes 75, a plurality of common electrodes 76, and a plurality of stainless thin plates 77a and 77b. 
If a plurality of piezoelectric/electrostrictive actuators disclosed in the references 1 and 2 are used to control the operation of each of those actuators, each piezoelectric element requires a switching circuit that includes a transistor. The number of parts in the device thus increases unavoidably. This is why it has been difficult to reduce the device in size.
At the same time, JP 2000-289196 discloses an ink jet print head that includes a plurality of thin film transistor united with each corresponding piezoelectric actuator on an insulated substrate.
FIG. 18A is a perspective view of the ink jet print head 201 in the same document. FIG. 18B is a simplified across sectional view of the ink jet print head 201. The ink jet print head 201 comprises a body 206, a piezoelectric actuator 207 and an insulated substrate 208. The body 206 comprises a nozzle plate 203 including a small opening 202 as a nozzle, a pressure chamber material 204 configuring a pressure 210 chamber and a vibration plate 205. A thin film transistor circuit 209 transmitting an electric driving signal to the piezoelectric actuator 207, is configured on a surface of the insulated substrate 208 on which the piezoelectric actuator 207 vibrating the vibration plate 205 is mounted.
To make this ink jet print head, the thin film transistor 209 is formed on the insulated substrate in a conventional thin film transistor manufacturing process. The piezoelectric actuator 207 is formed next to the thin film transistor 209. After that, the body 206 including the vibrating plate 205, the pressure chamber material 204 and the nozzle plate 203 is formed. The vibrating plate 205 has a function as a common electrode of the piezoelectric actuator 207. The ink jet print head in the same reference can be reduced in size because the thin film transistor 209 is formed next to the piezoelectric actuator 209 on the insulated substrate, which is rigid.